By photosynthesis and decomposition of organic matter (stand litter and humus) and by respiration of plants and animals large amounts of carbon dioxide are constantly being removed from and returned to the atmosphere. These gigantic C02 flowswere in equilibrium over millions of years. Annual C02 gains and losses of the atmosphere balanced rather exactly, so that the atmospheric C02 level hardly changed. Since the beginning of industrialization this dynamic equilibrium between the reservoirs of atmosphere and (living and dead) biomass has been disturbed by the burningof fossil fuels and the deforestation of large areas. Every year more C02 now reaches the atmosphere than is taken out by photosynthesis. This leads to an increasing fraction of the greenhouse gas C02 in the atmosphere a major cause of gradual temperature increase and of climate change.